1. Field of the Invention
The invention relates generally to the field of treating osteochondral pathologies. More particularly, the invention relates to methods and apparatus for implanting a substance eluting porous substrate into a bony defect to promote repair of osteochondral lesions.
2. Discussion of the Related Art
Interventions for the treatment of chondromalacia and osteoarthritis include a variety of modalities, which include arthroscopic debriedment, microfracture techniques, intraarticular injection of medicaments, osteochondral transplants, and open surgical interventions such as chondrocyte transplantation via cell culturing techniques. None of these techniques has achieved the goal of offering a technically and economically feasible technique for promoting the growth of hyaline cartilage cells within osteochondral lesions.
Cartilaginous tissues covering the articulating ends of bones are composed of collagen, primarily Type II collagen and chondrocytes. These tissues are addressed surgically for indications such as chondral lesions of traumatic origin, and degeneration of the articular surfaces as in osteoarthritis.
Osteoarthritis is a degenerative condition of the articular surfaces of the joints often in areas where weight bearing or load bearing surfaces have lost their fluid retaining capacity. The fluid retaining capacity is provided by the proteoglycan component of the cartilage matrix that normally opposes the forces exerted on the ends of articulating bones. It is the biochemical capability of fluid that provides a cushion between these surfaces.
Chondromalacia is a condition of the articular cartilage, particularly the knee that describes the degeneration of the articular surfaces as seen in osteoarthritis. This descriptor indicates a fraying or fibrillation of the articular cartilaginous tissues. Chondromalacia proceeds from this fibrillated state to a complete denuding of the articular tissues leaving only the bony surface, which eventually erodes. This erosion proceeds into the bony structures.
Debriedment refers to the mechanical removal of compromised tissues using cutting and scraping instruments. In the early stages, chondromalacia can be treated by mechanical cutting of the frayed tissue by a bladed hand instrument or by high speed mechanical shavers in common use in arthroscopic surgery today. The condition can also be treated using thermal and laser techniques. None of these treatments reverses or stops the degenerative process. These treatments do nothing to repair tissues. These treatments seek to improve function or reduce pain by removing tissues that interfere with function of the joint.
Electrothermal and lasers approaches have been utilized to perform a thermal chondroplasty whereby the fibrillated cartilage surface is treated with heat to coagulate the fibrillated or non-intact cartilage tissue, thus sealing the articular cartilage surface, and thereby inhibiting further degradation of the cartilage matrix. The mechanical aspects of the knee joint are thus maintained with little change in articular function. The use of the laser for treatment of chondromalacia has focused on the ablative (cutting and removing) effects of the laser rather than the low temperature coagulative sealing effects of electrothermal energies.
Microfracture techniques are employed when the cartilage is completely gone from an area of the articular surface. This approach attempts to create a channel from the cancellous bone underlying the articular surfaces to the joint space in hopes that this access to the cancellous bone will provide an avenue for mesenchymal stem cells which are produced in the bone to migrate to the chondral lesions within the joint, thereby promoting the growth of chondrocytes in the area of the defect. This technique is still considered controversial despite its relatively widespread use because of the lack of definitive clinical data.
Osteochondral transplants attempt to replace the articular surface by using xe2x80x98plugsxe2x80x99 harvested from healthy non-weight bearing surfaces, and implanting them into recipient sites prepared in the target lesion. This technique is less than satisfying in that normal healthy tissues must be sacrificed to be placed in the defect which may result in a failure of the transplant leaving both donor/harvest site and target lesion with a significant bony insult.
Cell culturing techniques have been evaluated for several years with some success in terms of ameliorating patient""s symptoms. The primary technique consists of two procedures, the first of which is done to collect a patient""s chondrocytes as a biopsy sample. These xe2x80x9ccellsxe2x80x9d are then sent to a company that xe2x80x9cculturesxe2x80x9d the cells and xe2x80x9cgrowsxe2x80x9d them so that there is enough tissue to re-implant in the patient""s chondral lesion. In a second procedure the cultured cells are re-implanted into the chondral defect and a periosteal flap is utilized to contain the cells within the defect. The tissue that is seen some time after autologous transplantation is characterized as xe2x80x9chyaline likexe2x80x9d since the tissue contains chondrocytes but cannot be characterized as hyaline cartilage. Clinical results at a small number of centers show some benefits but the cost and difficulty associated with a xe2x80x9ctwo surgeryxe2x80x9d procedure leave much room for improvement in the treatment of this condition. New efforts at simplifying this procedure and reducing costs are underway but is unclear whether any of these will be any more successful in promoting hyaline cartilage growth.
For these reasons, it would be desirable to provide a method and apparatus for promoting chondrocyte growth that most closely replicates the normal articular cartilage with a procedure that is less expensive, less invasive and more efficacious.
A goal of the invention is to satisfy the above-discussed requirements of keeping costs and invasiveness low while simultaneously replicating the normal articular cartilage and achieving high effectiveness which, in the case of the prior art, are not simultaneously satisfied.
One embodiment of the invention is based on an implantable prosthesis for treating osteochondral pathologies, comprising: a porous substrate; and a substance positioned within said porous substrate that is elutable with regard to said porous substrate. Another embodiment of the invention is based on a surgical instrument, comprising a trocar having a proximal end and a distal end; a drill locatable within said trocar to prepare a subchondral bleeding bed for insertion of an implantable prosthesis, said drill having i) a flexible shaft that is extendable beyond said proximal end of said trocar and ii) a rigid tip that is simultaneously extendable beyond said distal end of said trocar, said rigid tip adapted to cut a recess into said subchondral bleeding bed for insertion of an implantable prosthesis; and an advancement mechanism adapted to apply pressure to said implantable prosthesis. Another embodiment of the invention is based on a method for treating osteochondral pathologies, comprising a method for treating osteochondral pathologies, comprising: positioning a distal end of a surgical instrument at a site targeted for subchondral implantation of an implantable prosthesis that carries an elutable substance; cutting a recess into a subchondral bleeding bed for insertion of said implantable prosthesis; and press-fitting said implantable prosthesis into said recess at said site and permitting said elutable substance to interact with said subchondral bleeding bed. Another embodiment of the invention is based on a method of making an implantable prosthesis for treating osteochondral pathologies, comprising: forming a cavity in a porous substrate; introducing a substance, which is elutable with regard to said porous substrate, into said cavity; and coupling a cap to said porous substrate to enclose said substance within said cavity.
These, and other goals and embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such modifications.